Odds supermodularity and the Luce rule

Abstract

We present a characterization of the Luce rule in terms of positivity and a new choice axiom called odds supermodularity that strengthens the regularity axiom. This new characterization illuminates a connection that goes unnoticed, and sheds light on the behavioral underpinnings of the Luce rule and its extensions from a different perspective. We show that odds supermodularity per se characterizes a structured extension of the Luce rule that accommodates zero probability choices. We identify the random choice model characterized via a stochastic counterpart of Plott (1973)'s path independence axiom, which strengthens odds supermodularity.